Yeah it's because of the different size. My dad found out the hard way it's a smaller pipe in the kit, but the muffler shop fit it up just fine for like $25 I think. I don't remember finding a kit for the 3.5" trucks because SLP doesn't offer their's anymore. But the 5.3 kit will work with some welding.Because the fitment on the chart says it will NOT fit my Yukon XL.